Novel Internal Emulsifiers for High Biocontent Sustainable Pressure Sensitive Adhesives

In this paper, two novel fully renewable internal emulsifiers have been successfully synthesized from epoxidized soybean oil and natural acids (adipic and pimelic acid) by a solvent-free and self-catalytic method. It is found that the emulsifiers show similar chemical structure and functions with typical petroleum based internal emulsifiers (dimethylol butanoic acid and dimethylol propionic acid), in which the hydroxyl groups act as a cross-linking and the carboxylic acid groups provide the ionic segment. These two novel internal emulsifiers were employed together with castor oil to prepare a series of high biocontent anionic waterborne polyurethane dispersions (PUDs). The unique structure of these two emulsifiers and their good compatibility with castor oil offer PUDs excellent storage stability. Additionally, the biocontent of the polyurethane are high up to 77.7%. Moreover, the adhesive properties of the biobased pressure sensitive adhesives (PSA) were comprehensively investigated by shear resistance, tack, and 180° peel strength test. The PSAs had a shear strength of 1.18 h to more than 100 h, a tack of 1.78–5.66 N, and a peel strength of 1.23–2.77 N/mm, all WPU PSA show good pressure sensitive adhesive properties, which would further expand the application of these novel vegetable oil-based waterborne PUDs.